In the field of printing inks, coating materials, etc. in which an oxidative polymerization-type resin is used as a constituent, a dryer is added as a curing accelerator for drying the resin. Metal salts of heavy metals such as cobalt, manganese, lead, iron, and zinc and various carboxylic acids (hereinafter these metal salts may be abbreviated as “metallic soaps”) are generally used as the dryers for these inks and coating materials.
Particularly, cobalt metallic soaps have excellent drying performance. However, when a large amount of cobalt metallic soap is used in order to obtain further improved drying performance, surface drying of an ink or a coating film proceeds at a very high rate, and this causes a problem in that wrinkling and shrinkage occur. One method proposed to obtain high drying performance while the occurrence of wrinkling and shrinkage is prevented is to use a curing accelerator that uses a combination of a cobalt metallic soap and bipyridyl (see, for example, PTL 1). This curing accelerator can prevent the occurrence of wrinkling and shrinkage and has high drying performance.
However, cobalt compounds have been listed in Group 2B “Possibly carcinogenic to humans” in the list of carcinogenic risks by the International Agency for Research on Cancer and are therefore feared to be carcinogenic. In addition, since metallic cobalt is a rare metal and its supply is unstable, cobalt metallic soaps have a high cost. There is therefore a demand for a curing accelerator that has high drying performance with a reduced amount of cobalt metallic soap used or with no cobalt metallic soap used.
As a method of preventing wrinkling and shrinkage without the use of a cobalt metallic soap, a drying accelerator (a curing accelerator) that uses a combination of a manganese metallic soap and bipyridyl has already been proposed prior to the disclosure of PTL 1 (see, for example, PTL 2). Although the drying accelerator described in PTL 2 has an advantage in that no cobalt metallic soap is used, a problem with the drying accelerator when it is used for a printing ink or a coating material is that drying time is long.
A combination of a fatty acid manganese salt and a specific amino alcohol has been provided as a curing accelerator that can be used with a practical drying time (see, for example, PTL 3 to PTL 6). However, curability comparable to that of cobalt metallic soaps has not been obtained.
One method provided for an oxidative polymerization-type compound containing a vegetable oil is to use a complex composed of a specific tetradentate ligand compound and a metal as a curing catalyst (see, for example, PTL 7). However, the above vegetable oil is limited to a vegetable oil containing 50% or more of phenol compounds such as anacardic acid, anagigantic acid, pelandjauic acid, ginkgoic acid, ginkgolic acid, cardanol, cardol, methyl cardol, urushiol, thitsiol, rhengol, and laccol, and one example of such a vegetable oil is a cashew nut shell liquid obtained from Anacardium occidentale. Specifically, the curing reaction using the above complex is a radical coupling reaction of phenoxy radicals formed by dehydrogenation of the phenol compounds, and therefore the above complex cannot be used for a system containing no phenolic compounds. In addition, since the complex is poorly soluble in organic solvents, it is difficult to extend the use of the above complex to general-purpose ink and coating material compositions. It is stated that the complex may be formed within a curing reaction system to perform the reaction. However, in this case, materials that are difficult to handle outdoors, such as aqueous hydrogen peroxide and ethylenediamine, must be used in the system, so that the versatility of the above complex is low.